The present invention relates to a compression ratio control for an internal combustion engine.
There is a growing demand for a remarkable reduction in fuel consumption in addition to excellent output power performance. In order to improve fuel economy, one effective measure is to increase compression ratio to enhance thermal efficiency. However, if the compression ratio is increased to a sufficiently high level, there occurs frequent knocking during engine operation with high load, particularly at low speeds with high load. In order to improve output performance, it is known as effective measure to employ a variable valve timing control system or a variable valve lift system. However, with these valve operating systems, the amount of intake air is increased, causing an increase in real compression ratio. As a result, the tendency of knocking to occur increases during operation at low speed with high load. The real compression ratio is expressed as a product of volumetric efficiency and apparent compression ratio. This term real compression ratio is used in the following description.
An object of the present invention is to provode a control for an internal combustion engine in which occurrence of knocking is prevented while the engine operates at high real compression ratio.